Surgical Critical Care: Mechanical Ventilation – Patient-Ventilator Dyssynchrony

Definition

• Patient-Ventilator Dyssynchrony: Inappropriate Timing & Delivery of a Mechanical Breath in Response to Patient Effort
  • Mismatch Between the Patient’s (Neural) Breath & Ventilator-Assisted (Mechanical) Breath
• Occurs When Any of the Requirements for Patient-Ventilator Synchrony are Not Met

Requirements for Patient-Ventilator Synchrony

• The Ventilator Provides Flow & Pressure as Soon as Patient Effort Begins
• The Level of Assistance Meets the Patient’s Respiratory Demand
• The Ventilator Assistance is Terminated When Patient Effort Ends

Adverse Effects

• Increased Work of Breathing
• Ventilator-Induced Lung Injury (VILI) – From Alveolar Overdistention
• Ventilator-Induced Diaphragmatic Dysfunction – From Excessive Unloading of the Diaphragm
• Patient Discomfort
• Excessive Sedation Requirements
• May Have Increased Length of Mechanical Ventilation & Increased Risk of Mortality

Categories

• Trigger Dyssynchrony
  • Triggering Delay – Excessive Time Delay Between Neural Initiation & Mechanical Breath
    • Incorrect Ventilator Settings
  • Ineffective Efforts – Patient Effort from Neural Initiation Fails to Trigger a Mechanical Breath
    • Trigger Sensitivity Too High
    • Low Respiratory Drive
    • Weak Inspiratory Muscles
    • High Resistance
    • High Auto PEEP
  • Autotriggering – Mechanical Breath Trigged with no Neural Initiation
    • Trigger Sensitivity Too Low
    • Coughing
    • Hiccups
    • Shivering
    • Seizures
    • Strong Cardiogenic Oscillators
    • Condensation in the Ventilator Circuit (“Rain Out”)
• Cycle Dyssynchrony
  • Premature Cycling (Breath Stacking) – Neural Inspiratory Time is Longer than the Ventilator Inspiratory Time
    • Double Triggering – Sustained Diaphragm Contraction After the Ventilator Has Cycled Off Inspiration Causes Decreased Proximal Airway Pressure that is Mistaken for Another Initiation, Triggering an Immediate Breath
      • Assisted Breath Precedes a Controlled Breath Back-to-Back
    • Entrainment (Reverse Triggering) – Control Breaths Stimulate Diaphragm Contraction, Triggering an Immediate Second Breath
      • Controlled Breath Precedes an Assisted Breath Back-to-Back
  • Delayed Cycling – Ventilator Inspiratory Time is Longer than the Neural Inspiratory Time
    • Delayed Opening of the Expiratory Valve
• Flow Dyssynchrony
  • Insufficient Flow Rate – Flow Rate Will Not Change but Increased Inspiratory Efforts Will Cause a Drop in the Pressure Curve (“Scooping Out” or “Pull Down” of the Pressure Curve Upstroke)
  • Excessively High Flow Rate – Discomfort from High Flow Rate Can Cause Activation of Expiratory Muscle (“Fighting” or “Bucking” the Ventilator)

Management

• Disconnect from Ventilator & Manually Bag the Patient if Necessary
• Patient Management:
  • Optimize Sedation
  • May Require Neuromuscular Blockade
  • Treat Any Defined Pulmonary Pathology
  • Ensure Appropriate Nutrition & Pain Control
• Ventilator Management:
  • Pressure-Controlled Ventilation May Decrease Risk for Dyssynchrony in Some Patients
  • Specific Changes:
    • Ineffective Breath – Decrease Trigger Sensitivity (Risk for Autotriggering) or Address Auto PEEP
    • Autotriggering – Increase Trigger Sensitivity
    • Double Triggering – Increase Ventilator Inspiratory Time (Decreased Flow Rate, Increased Tidal Volume or Add an End-Inspiratory Pause)
    • Insufficient Flow Rate – Increase Flow Rate
    • Excessively High Flow Rate – Decrease Flow Rate
  • *Ventilator Adjustments May Increase Risk of Other Types of Dyssynchrony or Cause Other Damage
• Relieve Any Endotracheal Tube Kinking or Obstruction